PPINPO - generates and returns the boundary of the
"intersection" polygon, which consists of all points that are
inside both the clip polygon and the subject polygon.
CALL PPINPO
(XCCP,YCCP,NCCP,XCSP,YCSP,NCSP,RWRK,IWRK,NWRK,URPP,IERR)
#include <ncarg/ncargC.h>
void c_ppinpo(
float *xccp,
float *yccp,
int nccp,
float *xcsp,
float *ycsp,
int ncsp,
float *rwrk,
int *iwrk,
int nwrk,
int (*urpp_)( float *xcra, float *ycra, int *ncra),
int *ierr)
- XCCP
- (an input array of type REAL) is the X coordinate array for the clip
polygon.
- YCCP
- (an input array of type REAL) is the Y coordinate array for the clip
polygon.
- NCCP
- (an input expression of type INTEGER) is the number of points defining the
clip polygon.
- XCSP
- (an input array of type REAL) is the X coordinate array for the subject
polygon.
- YCSP
- (an input array of type REAL) is the Y coordinate array for the subject
polygon.
- NCSP
- (an input expression of type INTEGER) is the number of points defining the
subject polygon.
- RWRK
- (a scratch array, dimensioned NWRK, of type REAL) is a real workspace
array. Because of the way in which they are used, RWRK and IWRK may be
EQUIVALENCEd (and, to save space, they should be).
- IWRK
- (a scratch array, dimensioned NWRK, of type INTEGER) is an integer
workspace array. Because of the way in which they are used, RWRK and IWRK
may be EQUIVALENCEd (and, to save space, they should be).
- NWRK
- (an input expression of type INTEGER) is the length of the workspace
array(s). It is a bit difficult to describe how much space might be
required. At the moment, I would recommend using NWRK equal to about ten
times the total of the number of points in the input polygons and the
number of intersection points. This situation will change with time; at
the very least, I would like to put in an internal parameter that will
tell one how much space was actually used on a given call, but I have not
yet done so.
- URPP
- is the name of a user-provided routine to process the polygon-boundary
pieces. This name must appear in an EXTERNAL statement in the routine that
calls PPINPO and the routine itself must have the following form:
SUBROUTINE URPP (XCRA,YCRA,NCRA)
DIMENSION XCRA(NCRA),YCRA(NCRA)
...(code to process a polygon boundary piece)...
RETURN
END
Each of the arguments XCRA and YCRA is a real array,
dimensioned NCRA; the former holds the X coordinates, and the latter the
Y coordinates, of a piece of the polygon boundary. It will be the case
that XCRA(NCRA)=XCRA(1) and YCRA(NCRA)=YCRA(1).
- IERR
- (an output variable of type INTEGER) is returned with the value zero if no
errors occurred in the execution of PPINPO or with a small positive value
if an error did occur. The value 1 indicates that a degenerate clip
polygon was detected, the value 2 that a degenerate subject polygon was
detected, and the value 3 that the workspace provided was too small;
values greater than 3 should be reported to the author, as they indicate
some problem with the algorithm. Currently, if IERR is returned non-zero,
one can be sure that no calls to URPP were executed; in the future, this
could change, but, in that case, there will be an internal parameter
allowing one to request the current behavior.
The C-binding argument descriptions are the same as the FORTRAN
argument descriptions.
The FORTRAN statement
CALL PPINPO (XCCP,YCCP,NCCP,XCSP,YCSP,NCSP,RWRK,IWRK,NWRK,URPP,IERR)
causes the formation of an intersection polygon (of the clip and
subject polygons) and the delivery of that polygon's boundary, piece by
piece, to the user-specified polygon-processing routine URPP.
Use the ncargex command to see the following relevant examples:
ppex01, tppack, c_ppex01.
To use PPINPO or c_ppinpo, load the NCAR Graphics libraries ncarg,
ncarg_gks, and ncarg_c, preferably in that order.
Online: polypack, ppdipo, ppditr, ppintr, ppplcl, ppppap, ppunpo,
ppuntr, ncarg_cbind.
Hardcopy: None.
Copyright (C) 1987-2009
University Corporation for Atmospheric Research
The use of this Software is governed by a License Agreement.